An organic light-emitting device is a device having a thin film containing a fluorescent organic compound interposed between an anode and a cathode, in which excitons of the fluorescent compound are generated by injecting electrons and holes (positive holes) from each electrode into the compound and the light emitted when these excitons return to the ground state is utilized.
In a research by Eastman Kodak Company in 1987 (Appl. Phys. Lett. 51, 913 (1987)), luminescence on the order of 1000 cd/m2 upon application of voltage on the order of 10 V was reported in relation to a device having a function separate type two-layer structure using ITO for the anode, and magnesium silver alloy for the cathode, respectively, and using aluminum quinolinol complex as an electron-transporting material as well as a light-emitting material and triphenylamine derivative as a hole-transporting material. Relevant patents include U.S. Pat. Nos. 4,539,507, 4,720,432, 4,885,211, etc.
Moreover, luminescence ranging from ultraviolet to infrared rays can be obtained by changing the kind of fluorescent organic compound, and, recently, studies on various compounds are actively conducted. For example, such studies are described in U.S. Pat. Nos. 5,151,629, 5,409,783, 5,382,477, Japanese Patent Application Laid-Open No. 2-247278, Japanese Patent Application Laid-Open No. 3-255190, Japanese Patent Application Laid-Open No. 5-202356, Japanese Patent Application Laid-Open No. 9-202878, Japanese Patent Application Laid-Open No. 9-227576, etc.
In addition to the organic light-emitting devices using low molecular materials as mentioned above, an organic light-emitting device using a conjugated polymer was reported by a group in Cambridge University (Nature, 347, 539 (1990)). This report confirms that luminescence occurs in a single layer film which is formed of poly(phenylene vinylene) (PPV) using a coating system. Related patents of the organic light-emitting device using conjugated polymer include U.S. Pat. Nos. 5,247,190, 5,514,878, 5,672,678, Japanese Patent Application Laid-Open No. 4-145192, Japanese Patent Application Laid-Open No. 5-247460, etc.
The latest progress in the organic light-emitting device is remarkable in this way, and the features thereof facilitate production of light-emitting devices imparted with high luminance at low applied voltage, diversity of luminescence wavelength, high-speed response, thin shape and lightweight, thereby suggesting possibility for a wide variety of applications.
However, there still remain many problems in respect of durability, such as change with the passage of time by prolonged use, degradation by atmospheric gas containing oxygen, humidity, etc. Furthermore, when the application to a full color display and the like is envisaged, optical output of further higher luminance or higher conversion efficiency, and luminescence in blue, green and red of high color purity are required under the present condition.
For example, although diamine compounds as a luminescent material were disclosed in Japanese Patent Application Laid-Open No. 2001-52868, blue luminescence of high color purity (chromaticity coordinate: x, y=0.14-0.15, 0.09-0.10) was not obtained. An example using a compound having the similar diamino structure was also disclosed in Japanese Patent Application Laid-Open No. 2001-196177, but the compound was used as a hole injection layer, and there was no description of the use as a light-emitting layer and light-emitting properties thereof such as luminescence color and efficiency.